potential of 00.46 V obtained by redox titration (5). The This paper reports measurements of the redox reaction rate for net positive charge of the silver electrode at the equilibrium the {2Fe-2S} protein puditaredoxin (Pdx) on bare and bekanapotential of Pdx reduction was found to aid the charge transmycin-modified silver electrodes. The electron turnover rates were fer between the metal and the negatively charged protein determined using electroreflectance (ER) and cyclic voltammetry (Pdx) molecule (4). To reduce Pdx on a gold electrode, it (CV). The measurements were analyzed with two kinetic models:
was necessary to neutralize the negative charge on the bare (1) strongly adsorbed protein layer and (2) freely diffusing proelectrode [E pzc ร
00.2 V vs sat. AgCl (6)] by MEA modifitein. For the adsorbed layer model, the rates obtained with ER cation (7). For the bare silver electrode, the cyclic voltwere almost two orders of magnitude greater than the rates obammetry (CV) response was detectable for approximately tained with CV. For the freely diffusing model, the rates determined by the two methods were similar, suggesting that this kinetic 1 h. To improve the stability of the response it is important model is more appropriate. Modification of the Ag electrode with to understand electron transfer (ET) on the molecular level. bekanamycin resulted in a negative 0.1-V shift of the Pdx formal As the first step, we attempted to establish the correct kinetic potential, but showed only a small increase in the observed redox model to describe the electrochemical measurements. The reaction rates. The measured rate constants were compared with kinetic model is crucial because it determines the relationthe predictions of the Marcus theory of electron transfer. แญง 1997 ship between the observed rate constant and the microscopic Academic Press description of ET between specific molecules and the elec-